The Metal Box originates from Super Mario 64 as a green ! Block that materializes after Mario activates its corresponding green Cap Switch at the Cavern of the Metal Cap. Upon being destroyed, it releases a Metal Cap that, after grabbing it, encases him in metal. He becomes more powerful, immune to all damage, and can walk underwater, but at the same time, becomes much heavier, sluggish, and unable to swim. These effects are similar the Metal Box's effects in the Super Smash Bros. series, except that Mario's voice is not suppressed, unless he is submerged underwater.

All green, red, and blue ! Blocks are replaced by red ? Blocks in the Nintendo DS remake of the game, Super Mario 64 DS. After activating them with the red ? Switch at the Rainbow Tower, they can be broken to release the Power Flower, which has different effects on each of the game's four playable characters. This power-up exhibits the same effects as the Metal Cap when picked up by Wario.

The Metal Box encases the character's body in metal when broken with a physical attack. When broken by Rosalina in Smash 4, her Luma is also metalized. However, when broken by Olimar, his Pikmin are not affected. In addition, only one Ice Climber can hit the box first, so only one can be metalized per box. Finally, Giga Bowser, Wario-Man, Mega Lucario, and Giga Mac are not affected by breaking Metal Boxes.

In all five games, breaking the Metal Box has the following effects:

The effects last 12 seconds, but the time limit decreases as the user takes damage, especially from fire attacks like Bowser's Fire Breath.

The fighter becomes 4.5× (3× in Melee) heavier than normal. However, weight independent attacks can ignore the weight boost; this includes any attack that has the bury, paralyze, or stun effects.

Slightly increases jump force, although usually not by enough to compensate for the gravity and fall speed increase. However, it does not affect gliding, floating, or Yoshi's double jump.

Doubles a character's falling speed, making recoveries harder, and more vulnerable to certain chain grabs. Certain characters with multiple double jumps will not gain any net vertical distance while under the effects of a Metal Box, as they will fall below where they had began the jump before being able to jump again.

Increases a fighter's knockback resistance by subtracting the amount of knockback taken from attacks by 30 units. Weak projectiles such as Link's Arrows, and most jabs, will merely deal damage without causing flinching if they don't deal more than 0 units of knockback. However, some attacks can ignore the knockback resistance, which includes any attack that has the bury effect.

Characters make metal sound effects when hitting a surface upon taking a step. However, the sound more closely resembles that of a thin sheet of metal, suggesting that the character isn't turned into metal, just covered with it.

Metal characters fought in Classic Mode remain metal for the entirety of the battle. In Melee, their stock icon has a distinctly darker, metallic look.

The Metal Box makes its Super Smash Bros. debut in Melee. If a projectile destroys the Metal Box, then no one will be metalized. Interestingly, Ness' dash attack destroys the box, but does not give him the metal status.

Metal characters make different distinctive metallic sounds while walking, running, and landing, depending on their weight. Lighter characters make a soft clanging noise, middleweights make a deeper one, and heavyweights make a far deeper and louder one. Heavy characters such as Ganondorf, Samus, and Link and light characters such as the Ice Climbers and Zelda all make middleweight stepping sounds, despite not being medium weight. However, Mewtwo does not make any sounds while metal, even after landing from a jump.

Characters can fight Metal Mario and/or Metal Luigi in Adventure Mode. In addition, they also fight a random metal character in Classic Mode. The Metal Box also appears as a collectible trophy.

First spotted in Super Mario 64, the Metal Box holds the power to turn your character briefly into heavy metal. Your mass is exponentially greater while metallic, making it difficult for others to throw you. Be careful, though: not only will you move a bit slower, but you'll also fall much more quickly than you ordinarily would.

The Metal Box appears again in Brawl with the nearly same properties it had in Melee, although it will not break when hit by projectiles. It also has an effect on the new ability to swim; while characters will not sink as Metal Mario did in Super Mario 64, they will submerge deeper after falling into the water. This technique is used to reach a secret area in the Glacial Peak level of the Subspace Emissary mode. In Classic Mode, the player might also fight a random metal character. The walking sound effect no longer changes depending on the characters' weights, so everyone has the same sound when walking.

A "Metal" option exists in Special Brawl, which gives every player a permanent Metal Box effect. Lastly, the Metal Box appears again as a collectible trophy.

A green box that transforms whoever attacks it into metal. In metal form, you're a lot heavier than normal, so middling and even strong attacks don't move you too much, and standard attacks won't even make you flinch. The time you spend in metal form decreases with the damage you take. In Super Mario 64, the weight of the metal form allowed you to walk underwater.

The Metal Box returns as an item. Its properties mostly remain the same as in previous Super Smash Bros. games. However, its duration can no longer be extended by picking up additional Metal Boxes. In the 3DS version, the metal coating is translucent rather than opaque, but in the Wii U version, the metal texture is both opaque and reflective, with the current stage being reflected on the character's body.

In Classic Mode, the player must also fight a random metal character. The Metal Box is also available as a red item in Smash Tour, giving players the ability to start a battle in metal form. The "Metal" option reappears in Special Smash in Super Smash Bros. for Wii U. Lastly, the Metal Box appears again as a collectible trophy.

This green box will make you the ultimate defensive character, turning you into solid metal for a short time. You won't flinch from enemy attacks, even in midair, and it is much harder to launch you. On the other hand, you fall like a brick. Getting hit will reduce the duration of this item.

Whack this box to turn into a metal you! You won't flinch when attacked - even in mid-air - and you'll be harder to launch. Now, the downsides: you'll move slower, fall faster, and recovering when you fall off a stage will be a nightmare. Also, it's only temporary, or lasts until you've taken a certain amount of damage.

The Metal Box reappears once again in Ultimate as an item. The effects are identical to Smash 4, though the metal effect appears to slowly take over the character rather than immediately applying as it did in previous titles, similar to Inkling's ink.

In Super Smash Bros. for Wii U, while the metal texture reflects the actual stage, it does not reflect it in real-time, instead reflecting a screenshot of the stage. For example, the metal texture will only show a reflection of the Boxing Ring's Smash Bros. variant, as opposed to the default Punch-Out!! theme.

Despite being replaced by red ? Blocks in Super Mario 64 DS, the Super Smash Bros. for Wii U trophy lists the game as one of the Metal Box's appearances.